Hybrid TransmissionA hybrid transmission that uses Toyota’s original power split device

Hybrid Transmission

The hybrid transmission consists of the power split device, the generator, the electric motor and the reduction gears, etc.The power from the engine is split into two by the power split device. One of the output shafts is connected to the motor and thewheels while the other is connected to the generator. In this way, the motive power from the engine is transmitted through tworoutes, i.e., a mechanical route and an electrical route.

An electronically controlled continuouslyvariable transmission is also provided, which canchange speed while continuously varying the rpmof the engine and the rpm of the generator andthe electric motor (in relation to vehicle speed).

THS II also reduces friction loss by about30% by using ball bearings in the transmissionand low-friction.

Power Split Device

The power split device uses a planetarygear. The rotational shaft of the planetary carrierinside the gear mechanism is directly linked tothe engine, and transmits the motive power tothe outer ring gear and the inner sun gear viapinion gears. The rotational shaft of the ring gearis directly linked to the motor and transmits thedrive force to the wheels, while the rotational shaftof the sun gear is directly linked to the generator.

EngineGenerator Motor

Pinion gear

Planetary gear

Sun gear (generator)

Planetary carrier (engine)

Ring gear(motor/power shaft)

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Actions of the Engine, the Generatorand the Motor

1) WHEN THE VEHICLE IS AT REST

The engine, the generator and the motor are stopped.

2) DURING START-UP

The vehicle starts moving using only the motor drive.

3) DURING ACCELERATION FROM START

The generator, which also has the function of an enginestarter, rotates the sun gear and starts the engine. Once theengine has started, the generator begins generating electricity,which is used for charging the battery and supplied to themotor for driving the vehicle.

4) DURING NORMAL DRIVING

For the most part, the engine is used for driving.Electricity generation is basically not necessary.

5) DURING ACCELERATION

During acceleration from the normal driving state, theengine rpm is increased and, at the same time, the generatorbegins generating electricity. Using this electricity andelectricity from the battery, the motor adds its driving power,augmenting the acceleration.

Output Enhancement Based onHigh-Speed Rotation of theGenerator

Because the maximum possible rpm of the generatorhas been increased, it can draw on higher engine rpm, therebyproducing higher output. As a result, the amount of electricitycreated by the generator is increased, and this increasedamount feeds the motor, thus leading to an increase in drivingpower.

Colinear graphing of planetary gear relationships

A linear relationship always exists between rotations perminute of the various gears on the vertical axis.

Generator rpm Engine rpmMotor rpm

(vehicle speed)

Hig

her

max

imum

rpm

Sun gear Carrier Ring gear

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EngineThe methodical pursuit of fuel efficiency improvement

Using an engine that synergistically works with motor output and achieving high-efficiency operation and comfortablecruising through the synergistic effect of high-torque motor output

High-Expansion Ratio CycleA 1.5-liter engine is used, which achieves high efficiency

by using the Atkinson Cycle, one of the most heat-efficient,high-expansion ratio cycles. Because the expansion ratio((expansion stroke volume + combustion chamber volume)/combustion chamber volume) is increased by reducing thevolume of the combustion chamber and the chamber isevacuated only after the explosion force has sufficiently fallen,this engine can extract all of the explosion energy.

*1 Expansion ratio: (expansion stroke volume + combustion chambervolume)/combustion chamber volume*2 Compression ratio (compression stroke volume + combustion chambervolume)/combustion chamber volume

Engine cross-sectional view

ATKINSON CYCLE

A heat cycle engine proposed by JamesAtkinson (U.K.) in which compression stroke andexpansion stroke duration can be set independently.Subsequent improvement by R. H. Miller (U.S.A.)allowed adjustment of intake valve opening/closingtiming to enable a practical system (Miller Cycle).

Thermal efficiency is high, but because thisengine does not easily provide high output it hasvirtually no practical application unless used with asupercharger.

High expansion ratio conceptual diagram

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In conventional engines, because the compressionstroke volume and the expansion stroke volume are nearlyidentical, the compression ratio ((compression stroke volume+ combustion chamber volume)/combustion chamber volume)and the expansion ratio are basically identical. Consequently,trying to increase the expansion ratio also increases thecompression ratio, resulting in unavoidable knocking andplacing a limit on increases in the expansion ratio. To getaround this problem, the timing for closing the intake valve isdelayed, and in the initial stage of the compression stroke(when the piston begins to ascend), part of the air that hasentered the cylinder is returned to the intake manifold, in effectdelaying the start of compression. In this way, the expansionratio is increased without increasing the actual compressionratio. Since this method can increase the throttle valveopening, it can reduce the intake pipe negative pressureduring partial load, thus reducing intake loss.

High Functionality

VVT-i (Variable Valve Timing-intelligent) is used tocarefully adjust the intake valve timing according to operatingconditions, always obtaining maximum efficiency. Additionally,the use of an oblique squish compact combustion chamberensures rapid flame propagation throughout the entirecombustion chamber. High thermal efficiency, coupled withreductions in both the size and weight of the engine bodythrough the use of an aluminum alloy cylinder block, and acompact intake manifold, etc., help improve the fuel efficiency.

Output Improvement

The engine's top revolution rate has been increasedfrom the 4,500 rpm in conventional engines to 5,000 rpm,thereby improving output. Moving parts are lighter, piston ringshave lower tension and the valve spring load is smaller,resulting in reduced friction loss. Furthermore, the increaseof 500 rpm produces faster generator rotation, increasing thedriving force during acceleration and further improving fuelefficiency.

VVT-i valve timing (conceptual diagram)

Performance curve

Combustion chamber shape

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System ControlPrecise real-time control — sensing the driver’s intentions

The system control of THS II maintains the vehicle at its maximum operating efficiency by managing the energy used by theentire vehicle, which includes the energy for moving the vehicle as well as the energy used for auxiliary devices, such as the air-conditioner, heaters, headlights and navigation system. The system control monitors the requirements and operating states ofhybrid system components, such as the engine, which is the source of energy for the entire hybrid vehicle; the generator, whichacts as the starter for the engine and converts the energy from the engine into electricity; the motor, which generates the drivepower for running the vehicle using the electrical energy from the battery; and the battery, which stores the electrical energygenerated through power generation by the motor during deceleration. It also receives braking information being sent via thevehicle’s control network, as well as instructions from the driver, such as the throttle opening and shift lever position. In otherwords, the system control of THS II monitors these various energy consumption statuses of the vehicle in real time and providesprecise and fast integrated control so that the vehicle can be operated safely and comfortably at the highest possible efficiency.

THS II SYSTEM CONTROL

Accelerator

Vehicle speed

Air conditioner

Shift lever position

Brakes

Battery

Engine

Generator

Motor

Engine output

Drive wheels

Motor output

Regeneration

Smart key Immobilizer system

Power supply

System control (conceptual diagram)

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System Start-up and StopLike modern jet planes, THS II hybrid vehicles use by-wire

control, in which the driver’s instructions are converted intoelectrical signals (through wires) to be used in integrated control.In by-wire control, system reliability is the highest control priority.When a smart key sends information indicating that the driverhas gotten inside the vehicle, the system power supply is turnedon.

First, whether or not the hybrid computer itself is functioningnormally is monitored, and an operational check is performedbefore the ignition button is pressed.

When the ignition button is pressed, the system checkswhether or not various sensors, the engine, the motor, thegenerator and the battery are functioning normally. Then, theswitches for the components in the high-voltage system, suchas the motor, the generator and the battery, are turned on, makingthe vehicle ready to run. This is the start-up control sequence.When the driver presses the ignition button again before leavingthe vehicle, the components in the high-voltage system aredisconnected and, after confirming that such systems are turnedoff, the hybrid computer shuts down.

Safety checks are also being carried out while the vehicleis moving, and, based on various types of information such aschanges in driving conditions, the system controls the vehicle sothat it can operate in an emergency mode in the unlikely event offailure in the hybrid system or lack of fuel.

Engine Power ControlEngine power control is the basic control mechanism of

THS II for always minimizing the energy consumption of the entirevehicle.

Based on the vehicle’s operating state, how far the driverhas depressed the acceleration pedal and the status signals fromthe battery computer, energy management control determineswhether to stop the engine and run the vehicle using the electricmotor only or to start the engine and run the vehicle using enginepower.

When first started, the vehicle begins to operate using themotor unless the temperature is low or the battery charge is low.To run the vehicle using engine power, the engine is first startedby the generator and at the same time, the system calculatesthe energy required by the entire vehicle. It then calculates therunning condition that will produce the highest efficiency forproducing this energy and sends an rpm instruction to the engine.The generator then controls the engine revolution to that rpm.The power from the engine is controlled by taking into accountthe direct driving power, the motor driving power from electricalgeneration, the power needed by the auxiliary equipment andthe charging requirement of the battery. By optimizing this enginepower control, THS II has advanced energy management for theentire vehicle and has achieved improved fuel efficiency.

Engine operating range

Torq

ue

Engine rpm

Good

Fuel efficiency

Poor

Engine operating range

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Driving ControlThe driving power of a vehicle with THS II is expressed as the

combination of the direct engine driving power and the motor’s drivingpower. The slower the vehicle’s speed, the more the maximum drivingpower is derived from the motor’s driving power. By increasing thegenerator rpm, THS II has made it possible to use the engine’smaximum power starting at slower speeds than was possible withthe current THS. It has also made it possible to significantly increasethe maximum drive power by using a high-voltage, high-output motorthat successfully improves power performance. Because the enginehas no transmission and uses a combination of the direct driving powerfrom the engine and the motor's driving power derived from electricalconversion, it can control the driving power by seamlessly respondingto the driver’s requirements, all the way from low to high speeds andfrom cruising with a low power requirement to full-throttle acceleration.(This is known as torque-on-demand.)

Additionally, the time required to start the engine duringacceleration from motor-only drive has been reduced by 40%, greatlyimproving the acceleration response. In order to eliminate shock duringengine start-up, the generator also precisely controls the stoppingposition of the engine’s crank. To ensure that the vehicle’s drivingpower is not affected even when a large load is applied, e.g., whenthe air-conditioner is turned on, precise driving power correction controlis carried out, achieving smooth and seamless driving performance.

Regenerative-brake Control

In THS II, the newly developed Electronically Controlled Braking System (ECB) controls the coordination between thehydraulic brake of the ECB and the regenerative brake and preferentially uses the regenerative brake; it also uses a high-outputbattery and increases the amount of energy that can be recovered and the range in which it can be recovered. The systemincreases overall efficiency and, thus, fuel economy.

Driv

ing

pow

er

Battery Motor

Generator Motor

Direct drive from engine

Running resistanceVehicle speed

Engine Battery

Motor drive power

Drive powerGen-

erator

Direct drive from engine

Brake pedal

depression

Brake pedal

depression

THS IITHS

Hydraulic brakingBraking

powerBraking

power

Regenerative braking

Regenerative braking

ECB effect

Expanded regenerative rangeHydraulic

braking

Driving power performance

THS II drive power (conceptual diagram)

Improved regenerative braking

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THS II’s Torque-on-Demand Control

Torque-on-Demand ensures that driving power is provided faithfully according to the driver's wishes under any drivingconditions. THS II has further expanded this concept and has added an enhanced driver assist function, which ensures safedriving.

1) MOTOR TRACTION CONTROL

In THS, the engine, the generator, the motor and the wheels are linked together via the power split device. Furthermore,most of the engine power is converted into electrical energy by the generator, and the high-output and high-response motor drivethe vehicle. Consequently, when the vehicle’s driving power changes abruptly, e.g., wheel slippage on icy or other slipperysurfaces and wheel locking during braking, a protection control similar to that used in conventional traction control is used toprevent abrupt voltage fluctuation and revolution increase of the planetary gear in the power split device. In THS II, we haveadvanced the parts protection function further and achieved the world’s first motor traction control by utilizing the characteristicsof a high-output, high-response motor. The goal of the motor traction control is to restore traction when wheel slippage on asnowy road is detected, for example, and inform the driver of the slipping situation. The basic requirement for safe vehicleoperation is firm traction between the tires and the road surface. Motor traction control helps the driver maintain this state.

2) UPHILL ASSIST CONTROL

This is another driver assist function that is unique to the high-output motor THS II. This function prevents the vehicle fromsliding downward when the brake is released during startup on a steep slope. Because the motor has a highly sensitive revolutionsensor, it responsively senses the angle of the slope and the vehicle’s descent and ensures safety by increasing the motor’storque.

Wheel-speed behavior at start-up on a snowy road

Spe

ed (

km/h

) / A

ccel

erat

or d

epre

ssio

n (%

)

Accelerator depression

Drive-wheel speed without control (slippage) Drive-wheel speed With control

Vehicle speed

Time (seconds)

Motor traction control

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Output EnhancementRaising output through acceleration and environmental performance compatibility

Acceleration Performance

INCREASED OUTPUT

Increasing the motor performance andraising the control voltage to 500V have improvedthe maximum output of the motor by 1.5 times from33kW to 50kW. Coupled with this improvement,an increase in the maximum revolution of thegenerator from 6,500 to 10,000 rpm has increasedthe electrical power supplied to the motor at lowto medium speeds, thereby increasing the motoroutput, and significantly boosted the systemoutput, which also includes the engine’s directdriving power. Furthermore, in the high-speedrange, the engine, which is capable of fasterrevolutions and higher output, has boosted thesystem output.

BETTER ACCELERATION PERFORMANCE

Especially as a result of improvements inoutput in the low to medium speed range, bothat-start acceleration performance and overtakingacceleration performance have drasticallyimproved. A performance level that exceeds thatof a 2.0-liter gasoline engine vehicle has beenachieved. High response and smooth accelerationbased on the high-output motor have beenimproved, further advancing the hybrid drivingexperience.

Good responsiveness

Shock-free & seamless

Continuous power

Acc

eler

atio

n (G

)

Vehicle with THS II

Current Prius

2.4l Camry with 4-speed automatic transmission

Elapsed time (seconds)

Acceleration sensation 50km/h —> 80km/h

Acceleration from start

Acceleration when overtaking

THS Prius (1.5l)

THS II Prius (1.5l)

Allion (2,0l)

THS Prius (1.5l)

THS II Prius (1.5l)

Allion (2,0l)

(seconds)

(seconds)

Acceleration performance (TMC data)

Driv

e sh

aft o

utpu

t (kW

)Vehicle speed (km/h)

THS II

THS

System output comparison (TMC data)

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Improved Environmental Performance

OVERALL EFFICIENCY

THS II has achieved higher efficiency by improving hybrid energy management control and making improvements to theregenerative coordinated brake control, both of which are designed to improve the energy efficiency of the entire vehicle.

When compared in terms of overall efficiency (well-to-wheel efficiency), which indicates the efficiency of the entire processstarting from the fuel manufacturing process, to the driving of a vehicle using that fuel, THS II’s efficiency is striking. Its overallefficiency value has reached a level that exceeds even that of an FCHV (fuel cell hybrid vehicle), which is highly efficient,representing one step closer to creation of the ultimate eco-car.

Through technology such as that found in THS II, Toyota is working on development to the next step, including how suchtechnology may apply to FCHVs, with an aim toward achieving even better efficiency.

EMISSIONS

According to Toyota’s in-house measurements, the emission level from a vehicle with THS II meets the Ultra-Low EmissionsLevel in Japan, as well as the planned zero-emission (ATPZEV) regulations in California, which are considered to be strictest inthe world, and Europe’s next-generation regulations (EURO IV).

40

Fuel efficiency

(well-to-tank)(%)

Vehicle efficiency

(tank-to-wheel)(%)

Overall efficiency (%)(well-to-wheel)

Recent gasoline car

Prius(before

improvement)

Prius(after

improvement)

Prius with THS II

Toyota FCHV

FCHV (target)

Natural gas-H2

Regen-eration

Control

Accessories

Electrical

Transaxle

Engine

Other

Energy efficiency improve-

ment

Fuel efficiency(%) x Vehicle efficiency(%) = Overall efficiency(%)

Overall efficiency

Note: The Japanese-market Prius was upgraded in August 2002.

Contribution to energy efficiency

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In-house Development and ProductionLeading the hybrid evolution through in-house development and production

Production Technology

Based on Toyota’s corporate philosophy of internally developing core technologies, we have positioned the engine and thepower split device, which form the basis of THS II, as well as electrical and electronic parts such as the generator and the powercontrol unit, as the core units essential to the new system and have developed and are producing these core parts in-house.

By undertaking the development and production of motors and electronic parts in-house, which was unheard of for anautomaker, Toyota brought the world’s first hybrid vehicle to market and plans to play a leading role in the evolution of hybridvehicles.

For example, in terms of production technology, we are working on improving the insulation performance of motors that runon high voltage, developing semiconductor transistor (IGBT) technology that supports large inverter output and improving solderingtechnologies to increase heat dissipation. The accumulation of these technologies is what has made THS II possible.

SOURCES OF MAJOR COMPONENTS

Engine Toyota Kamigo Plant

Motor & generator Toyota Honsha Plant

Power split device Toyota Honsha Plant

Power control unit (electronic parts) Toyota Hirose Plant

Battery Panasonic EV Energy – a joint venture of TMC and Matsushita Electric Industrial Co., Ltd.

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Specifications of new hybrid system

Cross-sectional view

*Maximum combined engine and hybrid battery output and torque constantly available within a specified vehiclespeed range (Toyota in-house testing)

I tem THS II THS

Engine

System*

Battery Type

Type

Type

Maximum output in kw (Ps)/rpm

1.5 L gasoline (high-expansion ratio cycle)

57 (78)/5,000 53 (72)/4,500

115 (11.7)/4,200

33 (45)/1,040-5,600

350(35.7)/0-400

74 (101)/120 or higher

65 (88)

421 (42.9)/11 or lower

378 (38.5)

115 (11.7)/4,200

Synchronous AC motor

50 (68)/1,200-1,540

400(40.8)/0-1,200

82(113)/85 or higher

82 (113)

478(48.7)/22 or lower

478 (48.7)

Maximum torque in N-m (kg m)/rpm

Maximum output in kw (Ps)/rpm

Maximum torque in N-m (kg m)/rpm

Maximum output in kW (Ps)/vehicle speed km/h

Maximum torque in N-m (kg m)/vehicle speed km/h

Torque at 22km/h in N-m (kg m)

Output at 85km/h in kW (PS)

Nickel-metal hydride

Motor

Specifications of New Hybrid System

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Compiled by: Toyota Motor Corporation, Public Affairs Division4-8 Koraku 1-chome, Bunkyo-ku, Tokyo, 112-8701 Japan

May 2003

www.toyota.co.jp